Ion energy and mass distributions of the plasma during modulated pulse power magnetron sputtering

Modulated pulse power (MPP) sputtering is a variation of high power pulsed magnetron sputtering (HPPMS) that overcomes the rate loss issue and achieves enhanced plasma ionization through modulation of the pulse shape, intensity, and duration. In this study, the principle and characteristics of MPP/HPPMS technique are first introduced. An electrostatic quadrupole plasma mass spectrometer installed parallel to the target surface has been used to examine the plasma properties, including time averaged ion energy and mass distributions of the positive ions, generated during sputtering a metal Cr target in pure Ar and Ar/N2 atmospheres using MPP and continuous dc power sources in a closed field unbalanced magnetron sputtering system. It was found that the MPP plasma exhibits a low ion energy peak at 1–2 eV and a short ion energy tail with the maximum ion energy affected by the peak current and power utilized on the cathode. A significantly increased numbers of single and double charged Cr and Ar ions were identified in the MPP plasma as compared to the dc plasma in pure Ar. The number of ions (ion flux) increased when the peak target power and current were increased. Besides single and double charged Cr, Ar and N ions, N3+, N4+, CrN+ and CrN2+ ion species were also identified in the MPP discharge with the introduction of N2 into the system. The ion energy distributions of ion species for the MPP plasma in Ar/N2 atmosphere exhibit similar peak values and tail distributions to those of the MPP plasma in pure Ar atmosphere. However, the energy tail extended toward higher energies due to the increased peak current and power on the cathode as the N2 flow rate percentage was increased in the system.